Can't add image to post (it's my first post, maybe I'm an idiot?)

I’m trying to make my first post and can’t add an image to it. I’ve clicked the upload/insert image button, but it appears to be grayed out and nothing happens (the add and remove link buttons are also grayed out). I’ve read through everything I can find in the help pages, but nothing has helped. I’m hoping it’s a simple setting that I just missed, or someone knows a solution to the problem. I have the image I want to use on my computer and in my WP library (uploading there was easy), and I was able to cut and paste a thumbnail from the library to the post. Thanks for your help.

I was going to paste a screen print here, but wasn’t able.